Higher-Order Modal Dispersion in Graded-Index Multimode Fiber

Previously, we proposed a field-coupling model for propagation in graded-index multimode fiber (MMF), analogous to the principal states model for polarization-mode dispersion (PMD) in single-mode fiber. That model was based on the concept of first-order principal modes, which have well-defined group delays that depend on the strength of the mode coupling. That first-order model predicts a linear relationship between the intensity waveforms at the MMF input and output. Here, we extend that model to account for higher order modal dispersion. The higher-order model predicts several effects analogous to higher-order PMD: pulse broadening, filling-in between peaks of the pulse response, depolarization and pattern blurring at the MMF output, and a nonlinear relationship between input and output intensity waveforms.